In the manufacture of semiconductor devices such as power semiconductor devices, it is common to insert (or mount) metal terminals into the exterior resin case at predetermined locations after the case is molded. (The method of inserting metal parts into a resin case, etc. after it is molded is referred to as “outserting.”)
The “outserted” metal terminals are wire bonded to the semiconductor chip mounted within the resin case. It should be noted that in order to ensure accurate wire bonding and sufficient bonding strength, it is necessary to secure the metal terminals to the resin case so that they are not displaced from their predetermined positions by the wire bonding operation. Therefore, the resin case has structures thereon for engaging the metal terminals so as to restrict their displacement.
There will now be described, with reference to FIGS. 10 and 11, an exemplary engaging structure that receives therein and engages a metal terminal 100 so as to limit displacement of the terminal (or secure it). Referring to FIG. 10, the metal terminal 100 having a wire bonding surface 108 is inserted into a resin case 102 in the direction indicated by the arrow. More specifically, the metal terminal 100 is inserted between a pair of protrusions 104 (an engaging structure) on the resin case 102. FIG. 11 shows the metal terminal 100 that has been inserted and engaged between the protrusions 104. It should be noted that after the insertion of the metal terminal 100, its wire bonding surface 108 is secured between a pair of wire-bonding-surface holding protrusions 106 on the resin case. Other methods or structures for securing a terminal frame, etc. are disclosed in JP-A Nos. 59-008399 (1984), 62-158389 (1987), 2002-231217, 60-223143 (1985), 2002-291135, 01-243383 (1989).
Accurate wire bonding on a metal terminal requires that the terminal be secured to the resin case, as described above. However, in order to secure the metal terminal to the resin case with sufficient force, it is not enough merely to insert the terminal in place between protrusions on the resin case (as described with reference to FIG. 11). Specifically, as shown FIG. 12, which is a cross-sectional view taken along line 12-12 of FIG. 11, there are gaps A, B, and C between the protrusions 104 and the metal terminal 100, which prevents the metal terminal 100 from being sufficiently secured to the resin case. Further, as shown in FIG. 13, which is a plan view of the view of FIG. 11, there are also gaps D between the metal terminal 100 and the wire-bonding-surface holding protrusions 106, which also serve to prevent securing of the terminal. These gaps A, B, C, and D cannot be eliminated due to process variations.
Refer now to FIG. 14, which is a view of the same cross section as FIG. 12. In order to firmly secure the metal terminal 100 to the resin case (or between the protrusions 104 thereon) 102, an adhesive 110 may be applied to fill the gaps (A, B, C, and D) described above. However, the application of an adhesive requires a considerable amount of work, and it takes time for the adhesive to harden. This complicates the manufacturing process, resulting in increased takt time. It has also been found that the adhesive may spread and adhere to wire bonding surfaces and solder bonding surfaces resulting in reduced product yield.
Another way to firmly secure the metal terminal 100 to the resin case 102, which is made of a thermoplastic resin, is to fuse the resin around the terminal 100 using heated metal pieces 112 as shown in FIG. 15. This causes the metal terminal 100 to be thermoplastically bonded and secured to the resin case 102. However, this method is disadvantageous in that since the metal terminal 100 is only partially bonded to the resin case 102, the securing force is insufficient. The temperature of the metal pieces 112 may be increased to more widely bond the metal terminal 100 to the resin case 102. However, this may cause the melting of unintended portions of the resin case 102, resulting in deformation and reduced strength. Furthermore, molten resin material may adhere to the wire bonding surface and solder bonding surface of the metal terminal 100 resulting in reduced product yield.